Heres the problem.Suppose a file name 1 is created and some data is written to it. After this another 512 files are newly created and written to. When the the 513th file is created and an fd_t opened for it, it results in 1's fd_t being replaced in the fd-lru with 513th file's fd_t. This is the correct behaviour resulting in all refs getting unref from the fd_t of 1 and the fd and all related state being freed.
But, in some workloads, some refs are still pending even after the fd_t is removed from LRU, resulting in the fd still being bound to the inode. In nfs3svc_remove_cbk, while removing the inode state, we also ensure that any fd_ts in the cache for this inode are also removed. While removing the fd_t, this situation where the fd_t has replaced with another, even while a ref remains on the fd_t, results in a crash in the fdcache_remove path in nfs3svc_remove_cbk. This happens because the fd_ctx_get results in a NULL value because the ctx was already deleted when this fd_t was removed from fd-lru earlier. This patch fixes the crash by introducing a NULL check.